1. Field of the Invention
The present invention relates to a microwave plasma generator for generating plasma by transmitting microwave, and processing surface of an object to form desired shapes by irradiating ions in the plasma to the object, and especially, to a microwave plasma generator which is preferable for obtaining high magnetic field intensity distribution exceeding electron cyclotron resonance magnetic field by using permanent magnet.
2. Description of the Prior Art
The prior art in the field of the above described kind of microwave plasma generator was disclosed in, for example, J. Vacuum Science and Technology, B9 (1), Jan./Feb. p. 26-28 (1991). In the above publication, description that a same magnetic field can be formed a permanent magnet as the magnetic field formed by a solenoid coil which is described on pages 29-33 of the above reference and is used as a first static magnetic field generating means. In the above example, the permanent magnet used in replacement of the solenoid magnetic field became huge.
The huge size of the permanent magnet causes various problems described hereinafter.
Firstly, production cost of the permanent magnet becomes high. Further, an attenuation ratio of magnetic field at a location separated from the permanent magnet is small, and a large magnetic field remains in the processing object. Accordingly, a problem is caused that the plasma generator using the permanent magnet is not suitable for processing of magnetic field sensitive material such as, for example, fabrication of magnetic material. Furthermore, spacial fluctuation in propagation and absorption of microwave is significant on account of small attenuation in intensity of magnetic field and mild slope in spacial magnetic field gradient with the huge magnet. When the magnet is used in an ion source, the magnetic field remains at the vicinity of ion extracting electrodes, and as a result of bending orbits of the ions, a problem that the ion beam becomes divergent is generated. Furthermore, when an object is irradiated with ion beams, it is necessary to neutralize the irradiated portion with the same amount of electrons in order to avoid bearing electric charge of the irradiated portion, but a problem is caused that sufficient amount of electrons can not be supplied to the center of the ion beam when the electrons are supplied from outside the ion beam because the electrons can hardly traverse the magnetic field.
Generally speaking, in view of the quality of plasma, ion temperature in the above case is high because the ions accelerated by a slope of plasma potential is thermalized because the plasma generated in a strong magnetic field by a first static magnetic field generating means are diverged in a magnetic field free region surrounded with surface magnetic field generated by a second static magnetic field generating means in order to make the plasma uniform in a large size area, and the majority of the generated ions traverse the magnetic field. Separation of ion species is caused depending on difference of cyclotron diameter in the magnetic field, additionally, when used in a plasma processing apparatus, a problem such that the plasma processing is not performed uniformly is caused because radicals generated simultaneously with the plasma are not homogenized by the electromagnetic field.